Did you have to unlock the phone to do that?
I called AT&T and they said that they don't have the unlock code since they don't even sell the device, but that it works on sims outside the US. She seemed to imply that it won't work on tmobile but that if I go outside the US, and just put a sim in, it will work without me having to unlock the phone in anyway.
Can anyone verify this?
I can verify that calls do work on t-mobile here in the US on the AT&T version of the Nexus S.. Data speeds were "edge" only though. You don't need an unlock code from AT&T. The Nexus S is "technically" carrier unlocked. I have also used a Digicel sim card in it also.. And just like the t-mobile sim.. voice calls worked but data was extremely slow.